Control device for electric rotating machine

ABSTRACT

A control device has a unit for selecting each of states of an inverter applying a voltage to a generator, a unit for predicting a first current of the generator, flowing at a second time elapsed by one control period from a first time, from a detected current and the state of the inverter at the first time, a unit for predicting a second current of the generator at a third time elapsed by one control period from the second time while using the first current as an initial value of the second current, from information indicating one selected state set at the second time, for each selected state, a unit for determining one state corresponding to the second current nearest to instruction, and a unit for setting the inverter in the determined state at the second time to control current of the generator.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application 2009-96443 filed on Apr. 10, 2009, sothat the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control device which controls acontrolled variable of a multiphase electric rotating machine bycontrolling a power inverting circuit having a plurality of switchingelements such that each switching element electrically connects ordisconnects one of a plurality of voltage applying portions, applyingdifferent voltages, to or from one of terminals of the machine.

2. Description of Related Art

A control device for a three-phase motor has been used. For example,this device performs a pulse width modulation (PWM) control, based ontriangular wave comparison, for the motor to control three phasecurrents, actually flowing through respective phase windings of themotor, to an instructed value under the feed-back control. In this PWMcontrol, an instructed value of phase voltages to be applied from aninverter to the respective phase windings of the motor is calculated,and switching elements of the inverter are operated based on thedifference between the level of a carrier signal shaped in a triangularwave and the instructed value.

However, when this PWM control is performed in an excessive modulationregion in which the instructed voltage value is higher than an inputvoltage of the inverter, levels of higher harmonic waves contained inthe output voltage of the inverter increase. In this case, the higherharmonic waves undesirably influence the response characteristics of thecurrent flowing through the phase windings of the three-phase motor.This problem is arisen because it is assumed in the design of a currentcontrol system that the output voltage of the inverter can be always setat the instructed value.

To avoid this problem, Published Japanese Patent First Publication No.2008-228419 proposes a model prediction control performed in a controldevice. In this control, a plurality of operating states of an inverterapplying a voltage to a three-phase motor are preset, a current expectedto flow through the motor is predicted from the output voltage of theinverter, set in one operating state, for each of the operating states,and the inverter is actually set in the operating state which minimizesthe difference between the predicted current and an instructed current.Therefore, because the inverter is operated so as to optimize thevariation of the predicted current, the problem described above can beavoided to a certain degree.

Published Japanese Patent First Publication No. 2006-174697 alsoproposes a control similar to this model prediction control.

However, the inventor of this application found out that, because theoperating state is set in one control period of time by predicting acurrent flowing through the motor in the next control period of time,the current actually flow through the motor cannot be controlled withhigh precision. To control the current under this model predictioncontrol with high precision, it is necessary in the present controlperiod to provisionally determine one operating state, to be set in eachof several control periods subsequent to the present control period, topredict a current of the motor for each of the provisionally-determinedoperating states, and to finally determine the operating state, to beset in the control period subsequent to the present control period, fromthe predicted currents. However, in the case of this prediction, theload of calculation on a computer is extremely increased.

SUMMARY OF THE INVENTION

An object of the present invention is to provide, with due considerationto the drawbacks of the conventional control device, a control devicewhich controls an electric rotating machine while predicting acontrolled variable of the machine according to the model predictioncontrol with high precision so as to reduce the volume of calculationrequired for the prediction.

According to a first aspect of this invention, the object is achieved bythe provision of a control device which controls a controlled variableof an electric rotating machine by controlling a power inverting circuitto be set in one of a plurality of controlled states and to apply acontrolled voltage, corresponding to the controlled state, to theelectric rotating machine, where the control device comprises a firstpredicting unit, a state determining unit, a control unit and a secondpredicting unit. The first predicting unit predicts the controlledvariable of the electric rotating machine from information, indicatingone controlled state set in the power inverting circuit, as a firstprediction result, while using a second prediction result as an initialvalue of each first prediction result, for each of the controlled statesset in the power inverting circuit. The state determining unitdetermines one controlled state from the first prediction resultscorresponding to the controlled states. The control unit controls thepower inverting circuit to be set in the controlled state determined bythe state determining unit. The second predicting unit predicts thecontrolled variable of the electric rotating machine as the secondprediction result from information, indicating the controlled statedetermined by the state determining unit before the prediction of thesecond prediction result.

With this structure of the control device, the second predicting unitpredicts, from information indicating the controlled state determined bythe state determining unit and set by the control unit at a firstrenewal time, the controlled variable corresponding to the controlledstate of the power inverting circuit to be set at a second renewal time.The controlled variable predicted by the second predicting unit is usedas the initial value of the controlled variable predicted by the firstpredicting unit. The controlled variable predicted by the firstpredicting unit corresponds to the controlled state of the powerinverting circuit to be set at a third renewal time.

To predict the controlled variable, appearing in the electric rotatingmachine at the third renewal time, with high precision on the assumptionthat the power inverting circuit set at one controlled state at thesecond renewal time maintains this controlled state during a controlperiod between the second and third renewal times, it is desired toobtain the controlled variable, appearing at a time near to the secondrenewal time as close as possible to the second renewal time, as aninitial value of the controlled variable appearing at the third renewaltime. However, it is impossible or difficult to actually detect thevalue of the control led variable at a time near to the second renewaltime. Further, because it is required that the controlled state of thepower inverting circuit to be set at the second renewal time has beenalready determined at the second renewal time from the controlledvariable predicted to appear at the third renewal time, it is physicallyimpossible or difficult to predict the controlled variable appearing atthe third renewal time with high precision.

In this invention, because the second predicting unit predicts thecontrolled variable, appearing in the machine at the second renewaltime, from information indicating the controlled state determined by thestate determining unit and set by the control unit at the first renewaltime, the first predicting unit can predict the controlled variableappearing at the third renewal time with high precision while using thepredicted controlled variable appearing at the second renewal time as aninitial value of the controlled variable appearing at the third renewaltime. That is, the control device can control the machine to be set inone controlled state appropriate to the machine at the second renewaltime.

Accordingly, the control device can predict the controlled variable ofthe machine according to the model prediction control with highprecision, while reducing the volume of calculation required for theprediction, and can appropriately control the power inverting circuitaccording to the predicted controlled variable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the structure of a control system having acontrol device for a motor generator according to the first embodimentof the present invention;

FIG. 2A shows the relation between voltage vectors of a controlledvoltage and controlled states of an inverter shown in FIG. 1;

FIG. 2B shows directions and lengths of the voltage vectors;

FIG. 3 is a block diagram of a predicting unit shown in FIG. 1;

FIG. 4 is a time chart of an actual current vector, voltage vectors andpredicted current vectors according to the first embodiment;

FIG. 5 is a time chart of an actual current vector, voltage vectors andpredicted current vectors in the prior art;

FIG. 6 is a flow chart showing the procedure of the current predictionand the determination of the controlled state performed in a controldevice shown in FIG. 1 according to the model prediction control; and

FIG. 7 is a view showing the structure of a control system having acontrol device for a motor generator according to the second embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the accompanying drawings, in which like reference numeralsindicate like parts, members or elements throughout the specificationunless otherwise indicated.

First Embodiment

FIG. 1 is a view showing the structure of a control system having acontrol device for a motor generator according to the first embodiment.

As shown in FIG. 1, a high-voltage battery 12 supplies a direct currentto a control system 11, the control system 11 converts this directcurrent into an alternating current of a controlled voltage Vc, and amotor generator 10 is driven by this alternating current to produce adriving torque. This power generating system including the generator 10,the system 11 and the battery 12 is, for example, mounted on a hybridvehicle. The generator 10 represents an electric rotating machine whosefeature is the presence of magnetic saliency. More specifically, thegenerator 10 is a three-phase interior permanent magnet synchronousmotor (IPMSM). This motor has a rotor, permanent magnets having salientpoles and being disposed around a shaft of the rotor so as to beprotruded from the shaft, a stator surrounding the rotor, and threewindings (i.e., a u-phase winding, a v-phase winding and a w-phasewinding) wound on the stator.

The control system 11 has an inverter IV, representing a power invertingcircuit, for producing the controlled voltage Vc from a supply voltageVDC of the battery 12 and supplying a three-phase electric current(i.e., a u-phase current Iu, a v-phase current Iv and a w-phase currentTw defined on the uvw coordinate system) having the controlled voltageVc to the generator 10 such that the current flows through the generator10 as a controlled variable of the generator 10, a voltage sensor 18 fordetecting the supply voltage VDC, a current sensor 16 for detecting thephase currents Iu, Iv and Iq, a rotational angle sensor 14 for detectinga rotational angle θ of the rotor of the generator 10 rotated inresponse to the phase currents, and a control device 20, composing a lowvoltage system, for receiving information of the rotational angle θ,information of the phase currents Iu, Iv and Iq, information of thesupply voltage VDC from the sensors 14, 16 and 18 through an interface(not shown), receiving information of a target torque Tr and controllingthe controlled voltage Vc of the inverter IV according to the receivedinformation to control the generator 10.

The inverter IV has u-phase switching elements ESup and ESun seriallyconnected with each other; v-phase switching elements ESvp and ESvnserially connected with each other, w-phase switching elements ESwp andSwn serially connected with each other, and diodes Dup, Dun, Dvp, Dvn,Dwp and Dwn connected with the respective switching elements inparallel. Each switching element is made of an n-p-n insulated-gatebipolar transistor (IGBT). The emitters of the switching elements ESup,ESvp and ESwp are connected with the collectors of the respectiveswitching elements ESun, ESvn and ESwn. The collectors of the switchingelements ESup, ESvp and ESwp are connected with the higher voltageterminal of the battery 12, while the emitters of the switching elementsESun, ESvn and ESwn are connected with the lower voltage terminal of thebattery 12. The anode of each diode is connected with the emitter of thecorresponding switching element. The connecting point of the elementsESup and ESun is connected with the u-phase stator winding of thegenerator 10. The connecting point of the elements ESvp and ESvn isconnected with the v-phase stator winding of the generator 10. Theconnecting point of the elements ESwp and ESwn is connected with thew-phase stator winding of the generator 10.

The control device 20 produces control signals Sgup, Sgun, Sgvp, Sgvn,Sgwp and Sgwn from the received information and transmits the signalsSgup, Sgun, Sgvp, Sgvn, Sgwp and Sgwn to bases of the respectiveswitching elements ESup, Esun, Esvp, Esvn, ESwp and Eswn of the inverterIV to invert the supply voltage VDC of the direct current into thecontrolled voltage Vc.

The device 20 operates the inverter IV to indirectly control the torqueactually produced in the generator 10 to the target torque Tr. Morespecifically, the device 20 operates the inverter IV to directly controlan alternating current, actually flowing through the generator 10, to aninstructed current required for the generator 10 to generate the targettorque Tr. That is, in this embodiment, although the device 20 controlsthe torque of the generator 10 as a final controlled variable, thedevice 20 directly controls an alternating current, actually flowingthrough the generator 10, to the instructed current to control thetorque of the generator 10.

Further, the inverter IV can be set in any of a plurality of controlledstates (or operating states). Each controlled state corresponds to apattern of on and off states of the switching elements. The currentflowing through the generator 10 depends on each controlled state of theinverter IV.

In this embodiment, the control device 20 controls the inverter IV to beset in one of the controlled states at a renewal time every controlperiod of time. More specifically, the device 20 predicts (i.e.,estimates in advance) a first current, expected to flow through thegenerator 10 at a second renewal time elapsed by one control period froma first renewal time, from information indicating the controlled stateof the inverter IV actually set at the first renewal time, while usingthe current actually flowing through the generator 10 in response to thecontrolled state set at the first renewal time as an initial value ofthe predicted current. Further, the device 20 predicts a second current,expected to flow through the generator 10 at a third renewal timeelapsed by one control period from the second renewal time, frominformation indicating one controlled state imaginarily set in theinverter IV at the second renewal time for each of the controlled statesimaginarily set in the inverter IV, while using the first predictedcurrent expected to flow through the generator 10 at the second renewaltime as an initial value of the second predicted current expected toflow through the generator 10 at the third renewal time. The device 20determines one controlled state corresponding to one second predictedcurrent, closest to the instructed current among the second predictedcurrents expected to flow through the generator 10 at the third renewaltime, as a controlled state to be actually set in the inverter IV at thesecond renewal time. This control is called a model prediction controlin this specification.

The control device 20 has a dq converting unit 22 for converting phasecurrents Iu, Iv and Iw detected in the sensor 16 into an actual current(i.e. an actual d-axis current Id and an actual q-axis current Iqdefined on the dq rotational coordinate system) Idq by using therotational angle θ of the sensor 14, a rotational speed calculating unit23 for performing a differential calculation for the rotational angle θwith respect to time to obtain an electrical angle rotational speed ω ofthe rotor of the generator 10, an instructed current setting unit 24 forsetting an instructed current (i.e., an instructed d-axis current Idrand an instructed q-axis current Iqr defined on the dq rotationalcoordinate system) Idqr from information of the target torque Tr, amodel prediction control section 30 for determining a voltage vector Vi(i=0,1, - - , 7) of the controlled voltage Vc, corresponding to thecontrolled state to be actually set in the inverter IV, from informationof the actual currents Id and Iq, the instructed currents Idr and Iqr,the rotational speed ω, the rotational angle θ and the supply voltageVDC, and a control unit 26 for producing the control signals Sgup, Sgun,Sgvp, Sgvn, Sgwp and Sgwn from the voltage vector Vi determined by thesection 30 and supplying the signals to the inverter IV to set theinverter IV in the controlled state corresponding to the determinedvoltage vector Vi.

The dq rotational coordinate system is rotated with the rotor of thegenerator 10. The d-axis of the system is set so as to be directed fromone S magnetic pole to the corresponding N magnetic pole in the rotor.The q-axis of the system is set to be orthogonal to the d-axis on aplane perpendicular to the rotation axis of the rotor. The originalpoint of this system is placed on the rotation axis of the rotor. Theunits of the control device 20 are operated every control period oftime.

FIG. 2A shows the relation between voltage vectors Vi of the controlledvoltage Vc and controlled states of the inverter IV, while FIG. 23 showsdirections and lengths of the voltage vectors Vi. As shown in FIG. 2Aand FIG. 23, the inverter IV is set in one of eight controlled states.When the switching elements Esun, Esvn and Eswn on the lower electricpotential side are set in the on state while the switching elementsEsup, Esvp and Eswp on the high electric potential side are set in theoff state, the control voltage Vc has the voltage vector V0. When theswitching elements Esup, Esvp and Eswp are set in the on state while theswitching elements Esun, Esvn and Eswn are set in the off state, thecontrolled voltage Vc has the voltage vector V7. In the case of thevoltage vectors V0 and V7, all phases of the generator 10 areshort-circuited, so that the value of the controlled voltage Vc is setat zero. Therefore, each of the voltage vectors V0 and V7 is called azero vector. In contrast, when at least one of the switching elementsEsun, Esvn and Eswn and at least one of the switching elements Esup,Esvp and Eswp are set in the on state, the controlled voltage Vc has oneof the voltage vectors V1 to V6 having lengths longer than zero.Therefore, each of the voltage vectors V1 to V6 is called a non-zerovector.

As shown in FIG. 2B, the voltage vector V1 obtained by setting only theswitching element Esup in the on state is directed toward the u phaseand has the positive value, the voltage vector V3 obtained by settingonly the switching element Esvp in the on state is directed toward the vphase and has the positive value, and the voltage vector V5 obtained bysetting only the switching element Eswp in the on state is directedtoward the w phase and has the positive value.

As shown in FIG. 1, the control section 30 has a controlled stateselecting unit 31 for producing the voltage vectors V0 to V7 frominformation of the supply voltage VDC and selecting each of the voltagevectors V0 to V7 as the controlled state of the inverter IVcorresponding to the selected voltage vector. Each voltage vector isdefined on the uvw coordinate system. A phase component of the voltagevector is expressed by the value VDC/2 when the corresponding switchingelement Esup, Esvp or Eswp is set in the on state, while the phasecomponent of the voltage vector is expressed by the value −VDC/2 whenthe corresponding switching element Esun, Esvn or Eswn is set in the onstate. For example, the voltage vector V0 is expressed by (−VDC/2,−VDC/2, −VDC/2), and the voltage vector V1 is expressed by (VDC/2,−VDC/2, −VDC/2).

The control section 30 further has another dq converting unit 32 forconverting each of the voltage vectors selected in the unit 31 into avoltage vector V(Vd, Vq), defined on the dq rotational coordinatesystem, by using the rotational angle θ.

The control section 30 further has a predicting block 33 for predicting,in a period between a first renewal time and a second renewal timeelapsed by one control period Tc from the first renewal time, a d-axiscurrent Ide and a q-axis current Iqe, expected to flow through thegenerator 10 at a third renewal time elapsed by one control period Tcfrom the second renewal time, from information produced in the units 22,23 and 32 and information indicating the controlled state of theinverter IV actually set at the first renewal time, and a controlledstate determining unit 34 for determining a controlled state, to be setin the inverter IV at the second renewal time, from the predictedcurrent of the block 33.

More specifically, the predicting block 33 predicts a first d-axiscurrent and a first q-axis current, expected to flow through thegenerator 10 at the second renewal time, from information indicating thecontrolled state determined in the determining unit 34 in the precedingcontrol period and actually set in the inverter IV at the first renewaltime and information indicating the rotational speed ω of the unit 23while using the actual currents Id and Iq of the unit 22 as initialvalues of the respective predicted currents. Further, the predictingblock 33 predicts a second d-axis current Ide and a second q-axiscurrent Iqe expected to flow through the generator 10 at the thirdrenewal time, on the assumption that the inverter IV is set in each ofthe controlled states selected in the unit 31 at the second renewaltime, from information indicating the rotational speed ω of the unit 23while using the first predicted currents Ide and Iqe as initial valuesof the respective second predicted currents Ide and Iqe. The predictingblock 33 predicts the current vector Idqe=(Ide, Iqe) each time the unit31 selects one controlled state.

In this current prediction, voltage equations (c1) and (c2):Vd=(R+pLd)Id−ωLqIq   (c1)Vq=ωLdId+(R+pLq)Iq+ωφ  (c2)are used. Variables Vd and Vq denote a d-axis voltage and a q-axisvoltage applied to the generator 10, variables Id and Iq denote a d-axiscurrent and a q-axis current flowing through the generator 10, theparameter R denotes the resistance of the armature winding, theparameters Ld and Lq denote the d-axis inductance and the q-axisinductance, and the parameter φ is a constant of armature windinglinkage magnetic fluxes. A differential operator p (i.e., d/dt) withrespect to time is used.

A differential equation (c3) of a differential term pId of the d-axiscurrent Id is obtained as a state equation by rearranging the terms ofthe equation (c1), and a differential equation (c4) of a differentialterm pIq of the q-axis current Iq is obtained as a state equation byrearranging the terms of the equation (c1).pId=−(R/Ld)Id+ω(Lq/Ld) Iq+Vd/Ld   (c3)pIq=−ω(Ld/Lq) Id−(R/Lq)Iq+Vq/Lq−ωφ/Lq   (c4)The combination of the equations (c3) and (c4) is expressed as follows:

${\frac{\mathbb{d}}{\mathbb{d}t}\left( \frac{Id}{Iq} \right)} = {{\begin{pmatrix}{- \frac{R}{Ld}} & {\omega\frac{Lq}{Ld}} \\{{- \omega}\frac{Ld}{Lq}} & {- \frac{R}{Lq}}\end{pmatrix}\begin{pmatrix}{Id} \\{Iq}\end{pmatrix}} + {\begin{pmatrix}\frac{1}{Ld} & 0 \\0 & \frac{1}{Lq}\end{pmatrix}\begin{pmatrix}{Vd} \\{Vq}\end{pmatrix}} + \begin{pmatrix}0 \\{- \frac{\omega\;\phi}{L}}\end{pmatrix}}$

From the currents Id and Iq flowing through the generator 10 in a firstcontrol period and the voltages Vd and Vq applied to the generator 10 inthe first control period, the block 33 predicts currents Ide and Iqeexpected to flow through the generator 10 in a second control periodsucceeding the first control period, on the assumption that the voltagesVd and Vq are applied to the generator 10 in the first control period,according to the equations (c3) and (c4). In this prediction, thedifference calculus is, for example, applied for the equations (c3) and(c4) to set discrete variables every control period and to predict thecurrents Ide and Iqe from the discrete variables.

The determining unit 34 calculates a value of a predicting function Jfrom the predicted currents Ide and Iqe of the block 33 and theinstructed currents Idr and Iqr of the unit 24, each time the voltagevector is selected in the unit 31, and determines one controlled statecorresponding to the value of the function J, indicating the highestlevel of prediction, as a controlled state to be actually set in theinverter IV at the second renewal time.

More specifically, the value of the function J(edq) is indicated by thesquared length edq²=(Idr−Ide)²+(Iqr−Iqe)² of the current differencevector (Idr−Ide, Iqr−Iqe) between the instructed current vectorIdqr=(Idr, Iqr) and the predicted current vector Idge=(Ide, Iqe).Although each component of the current difference vector becomespositive or negative, the squared length is always positive. In thiscase, the value of the function J can be increased with the differencebetween the vectors Idqr and Idqe. That is, when the prediction level isset to be lowered with the increase of the value of the function J, thefunction J can be defined such that the prediction level is lowered withthe increase of the difference in each component between the vectorsIdqr and Idqe. Therefore, the unit 34 determines the controlled state ofthe inverter IV such that the value of the function corresponding to thedetermined controlled state is minimized.

FIG. 3 is a block diagram of the predicting block 33, while FIG. 4 is atime chart of the actual current vector Idq=(Id, Iq), voltage vectors Vand predicted current vectors Idqe=(Ide, Iqe) according to thisembodiment.

As shown in FIG. 4, the voltage vector V of the controlled voltage Vcoutputted from the inverter IV is renewed under control of the controldevice 20 at a renewal time T (e.g., Tn, Tn+1, Tn+2, - - - ) everycontrol period of time Tc. As shown in FIG. 3 and FIG. 4, the block 33has a first predicting unit 33 a and a second predicting unit 33 b.

In response to the voltage vector V(n) actually set at the renewal timeTn of the first control period Tc(n), the actual phase currents Iu, Ivand Iw and the rotational angle θ(n) at the renewal time Tn are detectedin the sensors 14 and 16, the unit 33 b receives information of thevoltage vector V(n), information of the actual current vectorIdq(n)=(Id(n), Iq(n)) obtained from the actual phase currents andinformation of the angle θ(n). The unit 33 b predicts a current vectorIdqe(n+1)=(Ide(n+1), Iqe(n+1)), expected to flow through the generator10 at the renewal time Tn+1 of the second control period Tc(n+1) elapsedby one control period from the renewal time Tn, from the vectors V(n)and Idq(n) and the angle θ(n) while using the actual current vectorIdq(n) as an initial value of the current vector Idqe(n+1). The unit 33a predicts a current vector Idqe(n+2)=(Ide(n+2), Iqe(n+2)), expected toflow through the generator 10 at the renewal time Tn+2 of the thirdcontrol period Tc(n+2) elapsed by one control period from the renewaltime Tn+1, while using the predicted current vector Idqe(n+1) as aninitial value of the current vector Idqe(n+2), on the assumption thatthe inverter IV outputs the controlled voltage Vc of one voltage vectorindicated by the information of the unit 32 at the renewal time Tn+1 ofthe second control period Tc(n+1), each time the unit 31 outputs theinformation to the block 33. The prediction in the units 33 b and 33 aare performed each time the voltage vector V is actually set at onerenewal time.

In this embodiment, as shown in FIG. 4, the prediction of the currentvector Idqe(n+1) corresponding to the controlled state of the inverterIV set at the renewal time Tn+1 is performed for the calculation of theinitial value of the predicted current Idq(n+2) corresponding to thecontrolled state of the inverter IV set at the renewal time Tn+2.

To predict the current Idqe(n+2) with high precision on the assumptionthat the inverter IV set at one controlled state at the renewal timeTn+1 maintains this controlled state during the control period betweenthe renewal times Tn+1 and Tn+2, it is desired to obtain a current,flowing through the generator 10 at a time near to the renewal time Tn+1to the utmost, as an initial value of the predicted current Idqe(n+2).However, it is impossible or difficult to detect the current at a timenear to the renewal time Tn+1. Further, because it is required that thecontrolled state of the inverter IV to be set at the renewal time Tn+1has been already determined at the renewal time Tn+1 from the predictedcurrent Idqe(n+2), it is physically impossible or difficult toappropriately set the inverter IV at the renewal time Tn+1.

In this embodiment, because the current Idqe(n+1) is predicted frominformation of the controlled state (i.e., the voltage vector V(n))actually set in the inverter IV at the renewal time Tn, the current Idqe(n+2) can be predicted with high precision by using the currentIdqe(n+1) as an initial value of the current Idqe(n+2).

In contrast, in the prior art as shown in FIG. 5, to determine thecontrolled state (i.e., the voltage vector V(n+1)) of the inverter IV,to be set at the renewal time Tn+1, in the first control period beforethe renewal time Tn+1, the difference calculus is used to use the valueIdq(n) of the current, flowing through the generator 10 at the renewaltime Tn, as an initial value of the predicted current Idqe(n+1).Therefore, when the discrete calculation using the control period Tc isperformed, the current Idqe (n+1) can be predicted so as to intend theprediction of the current Idq(n+2) flowing at the renewal time Tn+2.However, it is not proper to use the current Idqe(n+1) as an initialvalue of the predicted current Idqe(n+2) required in the prediction.That is, the current Idqe(n+1) cannot be predicted with high precisionto predict the current Idqe(n+2) flowing at the renewal time Tn+2. Inthis case, to determine the controlled state of the inverter IV set inthe second control period subsequent to the first control period, it isoften required to predict a plurality of currents flowing in severalcontrol periods subsequent to the first control period and to determinethe controlled state of the inverter IV set in the second control periodby calculating the value of a predicting function, depending on both onepredicted current and an instructed current, for each of the predictedcurrents. Even in this conventional current prediction, when thecontrolled state set in the second control period is predicted based onthe prediction of a plurality of currents flowing in several controlperiods subsequent to the present control period, the inventor of thisapplication found out that the precision in the prediction of thecurrent in the prior art approaches the precision in the prediction ofthe current according to this embodiment.

An example of the current prediction and the determination of thecontrolled state will be described with reference to FIG. 6. FIG. 6 is aflow chart showing the procedure of the current prediction and thedetermination of the controlled state performed in the control device 20according to the model prediction control. This current prediction andcontrolled state determination is performed every control period of timeTc. At a renewal time placed at the start of each control period, thecontrol device 20 controls the inverter IV to be set in one determinedcontrolled state.

The procedure shown in FIG. 6 is performed in the units 33 and 34 in thefirst control period Tc(n). At step S10, the second predicting unit 33 breceives the rotational angle θ(n) detected in the sensor 14 andinformation indicating the actual currents Id(n) and Iq(n) detected inthe sensor 16. Further, the unit 33 b receives the voltage vector V(n)determined by the block 34 in the preceding control period Tc(n−1).

At step S12, the unit 33 b predicts the currents Ide(n+1) and Iqe(n+1),expected to flow through the generator 10 in the second control periodTc(n+1) subsequent to the first control period Tc(n), from therotational angle θ(n), the actual currents Id(n) and Iq(n) and thevoltage vector V(n). More specifically, the forward difference calculusis performed for the equations (c3) and (c4) while using discretevariables set at intervals of the control period Tc, and the predictedcurrents Ide(n+1) and Iqe(n+1) are calculated. In this prediction,values of the actual currents Id(n) and Iq(n) are used as initial valuesof the predicted currents Ide(n+1) and Iqe(n+1). The voltage vector V(n)is converted to a voltage vector Vdq(n)=(Vd(n), Vq(n)) defined on the dqcoordinate system. This prediction is expressed as follows:Vdq(n)=C(θ(n))·V(n)Ide(n+1)=A·Id(n)+B·Vd(n)+FIqe(n+1)=A·Iq(n)+B·Vq(n)+Fwhile using the rotational angle θ(n).

Then, the first predicting unit 33 a predicts the currents Ide(n+2) andIqe(n+2), expected to flow through the engine 10 in the third controlperiod Tc(n+2) subsequent to the second control period Tc (n+1), foreach of the voltage vectors Vi on the assumption that the inverter IV isset in the controlled state indicated by the voltage vector Vi at therenewal time Tn+1. More specifically, at step 814, a variable jspecifying the voltage vector is set at 0. At step S16, the voltagevector Vj selected in the unit 31 is expressed by the voltage vectorVj(n) which denotes a candidate for the voltage vector V(n) to beactually set in the inverter IV in the second control period Tc(n−1). Atstep S18, the currents Idej(n+2) and Iqej(n+2), expected to flow throughthe engine 10 in the third control period Tc (n+2), are predicted in thesame manner as the prediction at step S12 by using the rotational angleθ(n), the predicted currents Ide(n+1) and Iqe(n+1) and the voltagevector Vj(n+1). In this prediction, values of the predicted currentsIde(n+1) and Iqe(n+1) are used as initial values of the currentsIdej(n+2) and Iqej(n+2). The voltage vector Vj(n+1) is converted to avoltage vector Vdqj(n+1)=(Vdj(n+1), Vqj(n+1)) defined on the dqcoordinate system. This prediction is expressed as follows:Vdqj(n+1)=C(θ(n)+ωTc)·Vj(n+1)Idej(n+2)=A·Ide(n+1)+B·Vde(n+1)+FIqej(n+2)=A·Iqe(n+1)+B·Vqe(n+1)+Fwhile using the rotational angle θ(n) and the value Δθ=ωTc.

At step S20, it is judged whether or not the variable j is equal to 7.That is, it is judged whether or not the prediction of the currentsIdej(n+2) and Iqej(n+2) for all voltage vectors V0 to V7 has beencompleted. In the case of a negative judgment at step S20, the procedureproceeds to step S22. At step S22, the variable is incremented by one.Then, the currents Idej(n+2) and Iqej(n+2) for another voltage vector Vjare predicted at step S16 and step S18.

In contrast, in the case of an affirmative judgment at step S20, theprediction of the currents Idej(n+2) and Iqej(n+2) for all voltagevectors V0 to V7 has been completed. Therefore, at step S24, the unit 34determines one voltage vector, minimizing the predicting function Jamong the voltage vectors V0(n+1) to V7(n+1), as the voltage vectorV(n−1) to set the output of the inverter IV at the voltage vector V(n+1)during the second control period Tc(n+1). More specifically, thedifferential vector Edqj=(Idr−Idej(n+2), Iqr−Iqej(n+2)) between theinstructed current vector Idqr=(Idr, Iqr) of the unit 24 and thepredicted current vector Idqej=(Idej(n+2), Iqej(n+2)) is calculated, andthe squared length edq²=(Idr−Idej(n+2))²+(Iqr−Iqej(n+2))² of thedifferential vector is calculated as the value of the predictingfunction Jj(edq) for each value of the variable j. The voltage vectorVk(k=0, 1, 2, - - - or 7) corresponding to the predicting functionJk(edq) having the lowest value among eight values of the predictingfunctions J₀(edq) to J₇(edq) is determined as the voltage vector V(n+1).

Therefore, the unit 26 produces the control signals Sgup, Sgun, Sgvp,Sgvn, Sgwp and Sgwn according to the determined voltage vector V(n+1)and controls the inverter IV according to the control signals such thatthe inverter IV starts outputting the controlled voltage Vc having thedetermined voltage vector V(n+1) at the renewal time Tn+1.

Then, at step S26, the preparation for the determination of the voltagevector in the next control period is performed in the block 33. That is,the voltage vector V(n) is set as a voltage vector V(n−1), thedetermined voltage vector V(n+1) is set as a voltage vector V(n), thedetected rotational angle θ(n) is set as a rotational angle θ(n−1), andthe actual current vector Idq(n)=(Id(n), Iq(n)) is set as an actualcurrent vector Idq(n−1)=(Id(n−1), Iq(n−1)). The vectors V(n−1) and V(n),the angle θ(n−1) and the vector Idq(n−1) newly set are stored in amemory (not shown).

In this embodiment, the following effects can be obtained.

The controlled state (i.e., voltage vector V(n)) already determined soas to set the inverter IV in the determined controlled state during thefirst controlled period Tc(n) is used for the prediction of the currentsIde(n+1) and Iqe(n+1) expected to flow through the generator 10 duringthe second controlled period Tc(n+1) subsequent to the first controlledperiod. Accordingly, the current prediction in the model predictioncontrol can be performed with high precision.

The currents Id(n) and Iq(n) detected in the sensors 16 are further usedas initial values of the currents Ide(n+1) and Iqe(n+1), and thecurrents Ide(n+1) and Iqe(n+1) in the second controlled period Tc(n+1)are predicted in the first controlled period Tc(n). Accordingly, thecurrent prediction in the model prediction control can be performed withhigher precision.

The predicted currents Ide(n+1) and Iqe(n+1) expected to flow during thesecond controlled period Tc(n+1) are used as initial values of thecurrents Ide(n+2) and Iqe(n+2) expected to flow through the generator 10during the third controlled period Tc(n+2) subsequent to the secondcontrolled period, and the currents Ide(n+2) and Iqe(n+2) are predictedin the first controlled period Tc(n), on the assumption that theinverter IV is set in one controlled state (i.e., voltage vectorVj(n+1)) at the renewal time Tn+1, for each of the controlled states.The controlled state (i.e., voltage vector V(n+1)) of the inverter IV tobe set at the renewal time Tn+1 is determined from the currents Ide(n+2)and Iqe(n+2) predicted for each controlled state. Accordingly, thecontrolled state of the inverter IV in each control period can beappropriately determined.

In the process (e.g., step S12) for the prediction of the currentsIde(n+1) and Iqe(n+1) corresponding to the setting of the controlledstate (i.e., voltage vector V(n+1)) of the inverter IV at the renewaltime Tn+1, the detected currents Id(n) and Iq(n) are used as initialvalues of the currents Ide(n+1) and Iqe(n+1). In the process (e.g., stepS18) for the prediction of the currents Ide(n+2) and Iqe(n+2), thepredicted currents Id(n+1) and Iq(n+1) are used as initial values of thecurrents Ide(n+2) and Iqe(n+2). Therefore, these processes aresubstantially the same. Accordingly, the current predicting process canbe easily designed, and the processes can be executed by using the samepredicting elements (or arithmetic program).

Second Embodiment

In this embodiment, a torque actually generated in the generator 10 anda magnetic flux actually induced in the generator 10 are set ascontrolled variables of the generator 10 directly controlled by acontrol device, and a current representing a physical quantity, fromwhich the torque and the magnetic flux can be calculated, is predicted,in the same manner as in the first embodiment, by using the detectedcurrent to determine the controlled state (i.e., voltage vector V(n+1))of the inverter IV. The torque and the magnetic flux at the renewal timeTn+2 are predicted from the predicted currents Ide(n+2) and Iqe(n+2)expected to flow at the renewal time Tn+2. The control device controlsthe generator 10 such that the predicted torque and the predictedmagnetic flux approach instructed values of the torque and magneticflux.

FIG. 7 is a view showing the structure of a control system having acontrol device for the generator 10 according to the second embodiment.

As shown in FIG. 7, a control device 40 in this embodiment differs fromthe device 20 shown in FIG. 1 in that the device 40 has a modelprediction control section 50 composed of the block 33, a torque andmagnetic flux predicting unit 37, an instructed magnetic flux settingunit 38 and a controlled state determining unit 34 a, in place of thesection 30 of the device 20.

The unit 37 predicts a magnetic flux vector Φe=(Φde, Φqe) defined on thedq rotational coordinate system and a torque Te from the predictedcurrents Ide and Iqe of the block 33 according to the followingequations:Φd=Ld·Id+φ  (c5)Φq=Lq·Iq   (c6)T=P(Φd·Iq−Φq·Id)   (c7)where the parameter P denotes the number of pole pairs. In thisprediction, by setting variables Id and Iq at the predicted currents Ideand Iqe, the variables Φd, Φq and T are calculated as the predictedmagnetic flux components Φde and Φqe and the predicted torque Te.

The unit 38 has a magnetic flux map indicating the relation between atorque and a magnetic flux vector. The unit 38 receives the targettorque Tr and sets an instructed magnetic flux vector Φr=(Φdr, Φqr)corresponding to the target torque Tr according to the relation of themap. The vector Φr is set so as to satisfy the requirement of themaximum torque control and the like. In this maximum torque control, themaximum torque is generated in the generator 10 from the minimumcurrent.

The unit 34 a calculates a value of a predicting function J from thepredicted magnetic flux vector Φe, the predicted torque Te, theinstructed magnetic flux vector Φr and the target torque Tr each timethe unit 31 selects one voltage vector. Then, the unit 34 a determinesone controlled state corresponding to the value of the function J,indicating the highest level of prediction, as a controlled state (i.e.voltage vector V(n+1)) of the inverter Iv to be actually set in thesecond control period. More specifically, the torque difference ET=Tr−Tebetween the torques Tr and Te and the magnetic flux difference EΦ=Φr−Φebetween the flux vectors Φe and Φr are calculated, and the value of thefunction J(ET, EΦ) is indicated by the sum ET²+EΦ² of the squared torquedifference ET² and the squared magnetic flux difference EΦ². The unit 34a determines the controlled state of the inverter IV corresponding tothe minimum value of the function J among the values of the function J.

Therefore, in this control device 40, a physical quantity such as acurrent, from which controlled variables such as a torque and a magneticflux can be calculated, appears in the generator 10 such that thephysical quantity corresponds to the controlled state of the inverter IVset at each renewal time. As shown in FIG. 4, the physical quantityvector Idqe(n+1) corresponding to the controlled state (i.e., voltagevector V(n+1)) set at the second renewal time Tn+1 is predicted from thedetected physical quantity vector Idq(n) corresponding to the controlledstate (i.e., voltage vector V(n)) set at the first renewal time Tn.Then, on the assumption that one controlled state is set at the secondrenewal time Tn+1, the physical quantity vector Idqe(n+2) correspondingto the controlled state (i.e., voltage vector V(n+2)) set at the thirdrenewal time Tn+2 is predicted, by using the predicted physical quantityvector Idqe(n+1) as an initial value of the physical quantity vectorIdqe (n+2), for each of the controlled states set at the second renewaltime Tn+1. Then, the controlled state (i.e., voltage vector V(n+1))corresponding to one physical quantity vector Idqe(n+2), having thehighest predicting level among predicting levels of the physicalquantity vectors Idqe(n+2) corresponding to all controlled states, isdetermined to be appropriate to the generator 10 at the second renewaltime Tn+1.

Accordingly, even when the control device 40 predicts the physicalquantity different from the controlled variable, the device 40 cancontrol the controlled variable of the generator 10, in the same manneras in the first embodiment.

In this embodiment, because there is no detecting unit (i.e. hardware)for directly detecting the controlled variable (i.e., actual torque ormagnetic flux), the physical quantity (i.e., current) is predicted fromthe detected physical quantity (i.e., detected current). However, theengine control system shown in FIG. 7 may have a detecting unit fordirectly detecting the magnetic flux of the generator 10. In this case,the state equations of the magnetic flux:pΦd=−(R/Ld)Φd+ωΦq+Vd+Rφ/Vd   (c8)pΦq=−(ω/Lq)Φd−(R/Lq)Φq+Vq   (c9)are obtained from the equations (c3) and (c4) and the equations (c5) and(c6). The block 33 predicts the magnetic flux vectorΦdqe(n+1)=(Φde(n+1), Φqe(n+1)) and the magnetic flux vectorΦdqe(n+2)=(Φde(n+2), Φqe(n+2)) from the detected magnetic fluxes Φd(n)and Φq(n), the rotational angle θ(n) and the information of the voltagevector V(n) according to the equations (c8) and (c9). The unit 37calculates the predicted torque Te(n+2) from the vector Φdqe(n+2) andthe vector Idqe(n+2) according to the equation (c7). Therefore, the unit34 a can determine the voltage vector V(n+1) from the predicted magneticflux vector Φdqe(n+2) and the predicted torque Te(n+2). Accordingly, thecontrol device 40 receiving the detected magnetic flux and current cancontrol the controlled variables (i.e., magnetic flux and torque) of thegenerator 10, in the same manner as in the first embodiment.

Further, in this embodiment, the engine control system shown in FIG. 7may have detecting units for directly detecting the magnetic flux andthe torque of the generator 10, while detecting no current. In thiscase, in addition to the prediction of the magnetic flux, the torque ispredicted. Then, the voltage vector V(n+1) is determined from thepredicted magnetic flux vector Φdqe(n+2) and the predicted torque Te.Accordingly, the control device 40 receiving the detected controlledvariables (i.e., magnetic flux and torque) can control the controlledvariables of the generator 10, in the same manner as in the firstembodiment.

Modifications

In each embodiment, controlled variables (e.g., currents Ide(n+2) andIqe(n+2) or magnetic fluxes Φde(n+2) and Φqe(n+2)) are predicted foreach of all voltage vectors V0 to V7. However, controlled variables maybe predicted for each of the non-zero vectors V1 to V6 and one zerovector V0 or V7.

Further, in each embodiment, the predicting function J is indicated onlyby the difference between the predicted controlled variable and theinstructed controlled variable. However, the predicting function J maybe additionally indicated by the number of switching elements of whichthe on or off states set at the renewal time Tn are changed to the otherstates at the renewal time Tn+1.

Moreover, in each embodiment, the control variable or the physicalquantity (e.g., the currents Ide(n+1) and Iqe(n+1) or the magneticfluxes Φde(n+1) and Φqe(n+1)) expected in the second control period andthe control variable or the physical quantity (e.g., the currentsIde(n+2) and Iqe(n+2) or the magnetic fluxes Φde(n+2) and Φqe(n+2))expected in the third control period are predicted in the first controlperiod to determine the controlled state of the inverter IV set in thesecond control period. However, control variables or physical quantitiesexpected in several control periods subsequent to the first controlperiod may be predicted one after another to determine the controlledstate of the inverter IV set in the second control period. Even in thiscase, it is effective to predict the controlled variable or the physicalquantity in the first control period from the detected controlledvariable or the detected physical quantity.

Furthermore, in each embodiment, the actual current I=(Iu, Iv, Iw) isdetected in synchronization with each renewal time. However, the currentI may be detected at the middle time of the control period between therenewal time Tn, and the next renewal time Tn+1. Even in this case, itis effective to use the detected current as an initial value of thepredicted current Idqe(n+1) corresponding to the controlled state (i.e.,the voltage vector V(n+1)) set at the next renewal time Tn+1.

Still further, in each embodiment, the controlled variable (e.g., thecurrent Idqe (n+2)) at the renewal time Tn+2, elapsed by one controlperiod from the renewal time Tn+1, is predicted to renew the controlledstate of the inverter IV at the renewal time Tn+1. However, thecontrolled variable at a middle time of the control period between therenewal time Tn+1 and the renewal time Tn+2 may be predicted to renewthe controlled state of the inverter IV at the renewal time Tn+1.

Still further, the current is predicted as a controlled variable in thefirst embodiment to determine the controlled state of the inverter IVsuch that the predicted controlled variable approaches an instructedcontrolled variable, and the magnetic flux and the torque are predictedas controlled variables in the second embodiment to determine thecontrolled state of the inverter IV such that the predicted controlledvariables approach instructed controlled variables. However, only themagnetic flux or only the torque may be predicted as a controlledvariable to determine the controlled state of the inverter IV such thatthe predicted controlled variable approaches an instructed controlledvariable. Further, the current and the torque may be predicted ascontrolled variables. When no current is used as a controlled variable,a controlled variable or a physical quantity different from a currentmay be detected by a sensor.

Still further, in each embodiment, the difference calculus such as aforward difference calculus is used to set discrete variables in themodel prediction control applied in the continuous system. However, inplace of the difference calculus, the linear multistage model may beused to set discrete values in N stages (N≧2) in the model predictioncontrol, or Runge-Kutta method may be used to set discrete values in themodel prediction control.

Still further, in each embodiment, only the fundamental wave componentcontained in the current is considered to predict the current in themodel prediction control. However, the model considering higher harmonicwave components contained in the inductance and/or the induced voltagein addition to the fundamental wave component may be used. Further, thepresent invention is not limited to this model prediction control, but amap stored in a memory may be used. When the device 20 or 40 receivesthe voltage V=(Vd, Vq) and the electrical angle rotational speed ω asinput parameters of the map, the predicted current denoting an outputparameter of the map is determined from the map. The ambient temperaturemay be added as another input parameter of the map. The map indicatesthe relation between discrete values of the input parameters and valuesof the output parameter.

Still further, in each embodiment, the torque is set as the finalcontrolled variable of the electric rotating machine represented by thegenerator 10, regardless of whether the torque is predicted. However,the rotational speed or the like in the generator 10 may be set as thefinal controlled variable.

Still further, in each embodiment, the model of predicting the currentis used while disregarding iron loss caused in the generator 10.However, a model considering iron loss may be used.

As the electric rotating machine, the interior permanent magnetsynchronous motor is used in the embodiments. However, any synchronousmotor such as a surface magnet synchronous motor or a field windingsynchronous motor can be used as the electric rotating machine. Further,any induction electric rotating machine such as an induction motor orthe like may be used.

Further, the electric rotating machine is mounted on a hybrid vehicle inthe embodiments. However, the electric rotating machine may be mountedon any vehicle such as an electric vehicle. Further, the electricrotating machine is not limited to a primary engine of a vehicle, butmay be used as a secondary engine.

Moreover, positive and negative terminals of the high-voltage battery 12adopted as the direct current source are used as voltage applyingportions in the embodiments. However, output terminals of a converterboosting the output voltage of the battery 12 may be used as voltageapplying portions.

Furthermore, the switching elements of the inverter IV are used as apower inverting circuit in the embodiments to electrically connect ordisconnect each of a plurality of voltage applying portions, which applydifferent voltages, to or from each of terminals of the electricrotating machine through the switching elements. However, any powerinverting circuit having a plurality of switching elements may be usedon condition that the circuit electrically connects or disconnects eachof a plurality of voltage applying portions, which apply three differentvoltages or more, to or from each of terminals of the electric rotatingmachine through the switching elements. For example, the circuitdisclosed in Published Japanese Patent First Publication No. 2006-174697may be used.

1. A control device which controls a controlled variable of an electricrotating machine by controlling a power inverting circuit, having aplurality of switching elements connecting and disconnecting a pluralityof voltage applying portions applying different voltages with/fromterminals of the electric rotating machine, to be set in one of voltagevectors determined according to on and off states of the switchingelements, the controlled variable being at least one of an electriccurrent flowing through the electric rotating machine, a torque of theelectric rotating machine and a magnetic field of the electric rotatingmachine, wherein the control device comprises: a first predicting unitthat, when a plurality of controlled states of the power invertingcircuit corresponding to the voltage vectors are imaginarily set so asto set the power inverting circuit in each of the controlled states at asecond renewal time, predicts the controlled variable of the electricrotating machine for each of the imaginarily-set controlled states; acontrol unit that determines one controlled state of the power invertingcircuit, expected at the second renewal time, from the controlledvariable predicted by the first predicting unit and sets the powerinverting circuit in the determined controlled state at the secondrenewal time; and a second predicting unit that receives a presentcontrolled state already determined by the control unit to be used forthe power inverting circuit at a first renewal time preceding the secondrenewal time and predicts an initial value, to be used for theprediction performed by the first predicting unit, by using the presentcontrolled state, and wherein a value of the controlled variablepredicted by the first predicting unit relates to a time after a timerelating to the value predicted by the second predicting unit.
 2. Thecontrol device according to claim 1, wherein the second predicting unitreceives a detected value of either the controlled variable or aphysical quantity, from which a value of the controlled variable can becalculated, and predicts a value of the controlled variable or thephysical quantity, from which the value of the controlled variable canbe calculated, expected at the second renewal time of the controlledstate, set by the control unit, by using the detected value.
 3. Thecontrol device according to claim 2, wherein the control unit renews thecontrolled state of the power inverting circuit every control period oftime, and the first predicting unit predicts the controlled variableexpected at a third renewal time, elapsed by one control period of timefrom the second renewal time of the controlled state set by the controlunit, by using the value of the controlled variable predicted by thesecond predicting unit as the initial value.
 4. The control deviceaccording to claim 3, wherein the second predicting unit predicts thevalue of the controlled variable or the physical quantity, from whichthe value of the controlled variable can be calculated, at the secondrenewal time, elapsed by one control period of time from the firstrenewal time, by using both the controlled state adopted at the firstrenewal time and either the value of the controlled variable or thephysical quantity detected in synchronization with the first renewaltime.
 5. The control device according to claim 1, wherein the voltageapplying portions are a positive terminal and a negative terminal of adirect current source, and the power inverting circuit has the switchingelements which can connect each of the positive and negative terminalsof the direct current source with any terminal of the electric rotatingmachine.